The urinary system (or renal system) includes the kidneys, the ureters, the bladder and the urethra. The kidneys filter and process blood, secreting soluble wastes in the form of urine. Urine travels from the individual kidneys through their respective ureters and into the bladder before being expelled from the body through the urethra.
Proper functioning of the urinary system may be impaired by damage to any of its components. The ureters are particularly vulnerable due to their small, thin shape. A ureter may be damaged during a medical procedure, such as a hysterectomy or an ureteroscopy, or as a result of trauma, such as a high-speed vehicular accident or a penetrating abdominal injury. Tumors, both in the ureter and in surrounding tissues, may exert pressure that compresses the ureter. A ureter may become obstructed due to kidney stones that become lodged in the ureter and restrict or block the flow of urine. As the only conduit for urine to leave the kidneys, it is extremely important to preserve the flow of urine through the ureter. A blocked ureter may lead to serious medical conditions, such as hydronephrosis in the corresponding kidney.
The patency of a ureter may be maintained by inserting a ureteral stent (also known as a ureteric stent) into the ureter. A ureteral stent is a thin tube that creates a passageway through the ureter and ensures that urine can travel from the kidneys to the bladder. In addition to maintaining the flow of urine through the ureter, ureteral stents are also used to promote healing of the ureter, to dilate the ureter prior to a medical procedure and to bypass obstructions within the ureter.
While early ureteral stents were simple tubes, modern ureteral stents incorporate a number of design features to prevent complications such as migration and occlusion. The portions of a ureteral stent that extend into the kidney and bladder may be curved or coiled to prevent the stent from becoming displaced. Ureteral stents with curved or coiled ends are referred to as JJ stents, double J stents or pigtail stents. The exterior of a ureteral stent may include channels that provide paths for urine flow in addition to the central lumen of the ureteral stent. The channels ensure that the ureteral stent remains functional if the central lumen becomes occluded or blocked.
These designs may reduce stent failure, but do not address the pain, discomfort or irritation (also referred to as colic) that many patients experience in the kidney, bladder or groin region. Stent pain and discomfort may occur spontaneously, while urinating, during strenuous physical activity or during sexual intercourse. Patients who experience pain or irritation often go to the emergency room due to the intensity and location of the symptoms. Treatment frequently involves removal of the ureteral stent. If the underlying issue that necessitated placing the ureteral stent has not resolved, the patient will require insertion of a new stent. Hospital visits and repeat stenting procedures can result in substantial medical expenses for patients and insurers.
An early solution to patient discomfort was forming ureteral stents entirely out of silicone. Silicone ureteral stents were well-tolerated by patients, but medical professionals found these stents difficult to handle and insert due to their lack of rigidity. As a result, silicone ureteral stents were phased out of the market.